An example of a known control valve (see Patent Document 1) for a variable displacement compressor that is used for compressing refrigerant in an air conditioner of an automotive vehicle is a control valve having a pressure sensitive part that imparts a biasing force to a moving member in accordance with the pressure introduced to the pressure sensitive part, and moves the moving member by the biasing force to adjust the valve opening. The control valve uses a bellows assembly in the pressure sensitive part, and FIG. 6 is a schematic cross-sectional view of such a control valve for a variable displacement compressor.
The control valve 1 is composed of a solenoid part 2, a valve portion 3, and a bellows assembly 4, as shown in FIG. 6. The solenoid part 2 is disposed at one end of a cylindrical valve body 5, generates a magnetic force by supplying an electric current to a coil 6, moves the movable iron core 7 to the fixed iron core 9 side disposed in the leftward direction against a spring 8, and imparts a biasing force having a magnitude proportional to the square of the direct current value to a valve rod 10. A port 11 that is in communication with a discharge pressure Pd area of the variable displacement compressor, and a port 12 that is in communication with an inner chamber (chamber pressure Pc) of the variable displacement compressor are formed on the valve body 5, and a valve portion 3 is configured so that the flow rate of the discharge refrigerant gas that flows toward the inner chamber of the compressor can be adjusted based on the valve opening in relation to the valve seat 14 of the valve element 13 formed at the end portion of a valve rod 10.
In contrast, a bellows assembly 4 is disposed in a pressure sensitive chamber 16, which is composed of a case 15 and the valve body 5, at the other end portion on the opposite side of the solenoid part 2 of the valve body 5 constituting the pressure sensitive part 16, and a suctioning pressure Ps of the compressor acts on the pressure sensitive chamber 16. The bellows assembly 4 has a bellows 19 in which both sides are retractably held by holders 17, 18. A spring 20 is mounted between the two holders, and a connecting rod 21 is disposed between the holder 18 and a left end 10a of the valve rod 10, connected in direct contact with the two members. Therefore, the bellows 19 expands and contracts in accordance with variations in the suctioning pressure Ps introduced to the pressure sensitive chamber 16, the biasing force acting on the valve rod 10 varies, and the valve opening becomes variable.
The balance formula Ps=(F1+F2−F)/A of the force that operates on the valve rod 10 applies when the control valve 1 configured in this manner is open, wherein F1 is a biasing force of the spring 20, F2 is the biasing force of the spring 8, F is a solenoid thrust, and A is an effective pressure receiving surface area of the bellows. It is apparent from the formula that the suctioning pressure Ps is balanced at a low value when the solenoid thrust F is increased, and conversely, the suctioning pressure Ps is balanced at a high value when the solenoid thrust F is reduced. Therefore, [the control valve 1] is widely used as a control valve for variable displacement compressors that are used for compressing refrigerant in air conditioners.    Patent Document 1: Japanese Laid-open Patent Application No. 2001-141086 (paragraphs 0015 to 0018, and FIGS. 1 and 4)